The market for displays and other devices (e.g., keyboards) having non-mechanical touch functionality is rapidly growing. As a result, touch-sensing techniques have been developed to enable displays and other devices to have touch functionality. Touch-sensing functionality is gaining wider use in mobile device applications, such as smart phones, e-book readers, laptop computers and tablet computers, all of which include display units for displaying information and for interacting with a user.
Touch systems in the form of touch sensors have been developed that respond to a variety of types of touches, such as single touches, multiple touches, and swiping. Some of these systems rely on light-scattering and/or light attenuation based on making optical contact with a touch-screen surface, which remains fixed relative to its support frame. An example of such a touch-screen system is described in U.S. Patent Application Publication No. 2011/0122091.
Some touch sensors rely on the principle of Total Internal Reflection (TIR) to guide light within a thin sheet of transparent material. Light is conveyed within the thin sheet between sets of light sources and detectors operably disposed about the periphery of the sheet. A finger or other implement that touches the surface of the thin sheet will typically interact with the evanescent portion of internally reflected and transmitted light that extends just beyond the surface of the sheet. This causes attenuation of the guided light by what is called “frustrated TIR” or FTIR.
In some instances, touch screens are interfaced with an underlying display unit to form a touch-sensitive or touch-sensing display. The touch screen usually needs to be separated from the underlying display unit by an air gap so that the display unit does not interfere with the TIR propagation of light within the transparent sheet and cause attenuation. Bonding the touch screen to a liquid-crystal display (LCD), for example, would cause most of the guided light to leak into the LCD, where it is then absorbed or scattered. Yet, there are many applications where bonding the touch screen directly to another member such as a display unit or support substrate would be beneficial.